Method of processing metal parts by blanking

ABSTRACT

A method of processing metal parts and the like by blanking includes the steps of performing a first blanking step on a semi-finished product in order to produce a blanked semi-finished product, and performing a subsequent processing of the blanked semi-finished product to produce a finished product. The first blanking step is performed leaving an allowance on the blanked semi-finished product, and wherein the subsequent processing includes at least one second blanking step by which the allowance is removed from the blanked semifinished product.

TECHNICAL FIELD

The present invention relates to a method of processing metal parts andthe like by blanking according to the preamble to main claim 1.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

According to the prior art, the blanking of metal parts in a press, alsoknown as punching, is an operation which brings about the detachment ofa portion from a semi-finished product along an outline corresponding tothe cross-section of a blanking tool, that is the punch, and of arespective die. The cutting takes place owing to the pressure exerted bythe punch during its working stroke on the semi-finished productdisposed on the die.

Blanking is widely used in various fields by virtue of the low costs andfast production that are typical of this process. However, it has somedisadvantages such as, for example, poor surface finishing of at least aportion of the detachment region. In fact a portion of the surfaceresulting from blanking has imperfections such as signs of tearing andthe like which are not acceptable in the finished product in some cases.Generally, about ⅓ of the surface produced during blanking is cut andthe remaining ⅔ is torn so that the part has to be reprocessed byfurther finishing processes, for example, beveling or polishing, toattenuate the above-mentioned surface imperfections. However, theseoperations lead to a considerable increase in processing costs.

BRIEF SUMMARY OF THE INVENTION

The problem underlying the present invention is that of providing amethod of processing metal parts by blanking that is designed toovercome the limitations discussed above with reference to the prior artmentioned.

This problem is solved by the present invention by means of a method ofprocessing parts by blanking in accordance with the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics and the advantages of the invention will becomeclearer from the following detailed description of a preferredembodiment thereof which is described by way of non-limiting examplewith reference to the appended drawings, in which:

FIG. 1 is a perspective view of a semi-finished metal product to beprocessed in accordance with the method of the invention,

FIG. 2 is a perspective view of the semi-finished product of FIG. 1after a first processing step,

FIG. 3 is a is a perspective view of the semi-finished product of FIG. 2after a further processing step,

FIG. 4 is a perspective view of the semi-finished product of FIG. 3after a further processing step,

FIG. 5 is a perspective view of the semi-finished product of FIG. 4after a further processing step, and

FIG. 6 is a schematic view of a detail of the semi-finished product ofFIG. 3, in section and on an enlarged scale.

PREFERRED EMBODIMENT OF THE INVENTION

With reference first of all to FIG. 1, a semi-finished product 1 made ofa metal such as, preferably, brass, nickel silver, aluminium, preciousmetals, or the like, is prepared for processing according to the methodof the invention.

The drawings show a semi-finished product for the production of aspectacle frame; however, the method according to the invention isdirected towards the processing of semi-finished products irrespectiveof their final purpose and can therefore be used in various technicalfields, such as goldsmithery, precision mechanics, spectacle production,etc.

According to the method of the invention, the semi-finished product 1,which has a predetermined shape produced by conventional blanking or bystamping, is first of all processed by coining to produce a coinedsemi-finished product 10, on one surface 2 of which an imprint 3 of theshape of the finished product to be produced is coined. The imprint 3 ispreferably formed in high relief.

The coined semi-finished product 10 is shaped as a portion of aspectacle frame and, in particular, comprises two upper portions oflens-holding rims 5 connected by a bridge 7, and two shoulders 6.

A plurality of projections is also formed on the surface 2 of the coinedsemi-finished product 10 by the coining step; in this preferred example,a first and a second pair of appendages 4 a, 4 b are formed for locatingthe coined semi-finished product 10 on a die (not shown) for thesubsequent blanking step.

The coined semi-finished product 10 is then subjected to a firstblanking step by means of a conventional die and punch, so as to producea blanked semi-finished product 20 having the characteristics describedbelow.

During this first blanking step, the coined semi-finished product 10 isblanked, leaving an allowance which affects its entire blanking profileor at least the surfaces that are visible in the finished product. Inpractice, the die and the punch are larger than is necessary forblanking to finished dimensions, by an amount equal to a preselectedallowance. According to a principal characteristic of the invention, thethickness S of the allowance is between 0.1 and 1 mm, and preferablybetween 0.2 and 0.25 mm.

Moreover, during the first blanking step, the first pair 4 a of locatingappendages of the coined semi-finished product 10 is removed.

The surface blanked in this first blanking step, in which the blankedsemi-finished product 20 is produced, has the typical imperfections dueto blanking; that is, a generally major portion of the thickness bearssigns of tearing.

The blanked semi-finished product 20 is then blanked for a second timeso as to produce a final product 30 of the desired dimensions. In thissecond blanking step, the allowance remaining after the first blankingand also the second pair of locating appendages 4 b are removed.

Surprisingly, it has been found that the number and density ofimperfections of the surface of the final product 30 that is involved inthe second blanking are greatly reduced in comparison with thesemi-finished product 20 produced by the first blanking step so that theblanked surface is homogeneous and substantially free of signs oftearing.

It is pointed out that the second pair of appendages 4 b is preferablyformed in surfaces of the semi-finished product that can be processedfurther after the second blanking step and/or which are not in view inthe finished product; in the example described, which relates to aproduct that is intended to constitute the front portion of a spectacleframe, the second pair of appendages 4 b is formed on the inside of thelens-holding rim portions 5. In the region of these projections, theblanked surface portion of the final product 30 bears signs of tearingand more marked imperfections than the remaining surface since it issubjected to a single blanking step, but a chamfering step issubsequently performed on the inside of the lens-holding rim 5 for thefixing of the lenses to the spectacle frame and the surface portionaffected by the locating appendages 4 b is therefore reprocessed.

In order also to remove the remaining irregularities, the final product30 may be polished, for example, by tumbling until the desired surfaceuniformity is achieved, as shown, for example, in FIG. 5 in which afinal polished product is indicated 40.

The invention thus solves the problem posed, affording many advantagesover the prior art mentioned.

A first advantage consists of the fact that, by virtue of the method ofthe invention, the final product has a surface finish which isconsiderably improved in comparison with a semi-finished productconventionally blanked only once. In particular, the surface portionwhich may bear signs of tearing is considerably smaller.

Moreover, the method of the invention permits production with limitedcosts, lower than those of production by other methods which give anequally homogeneous surface.

1. A method of processing metal parts and the like by blanking, themethod comprising the steps of: performing a first blanking step on asemi-finished product in order to produce a blanked semi-finishedproduct, and performing a subsequent processing of the blankedsemi-finished product to produce a final product, wherein the firstblanking step is performed leaving an allowance on the blankedsemi-finished product, and in the subsequent processing comprises atleast one second blanking step by which the allowance is removed fromthe blanked semi-finished product.
 2. The method according to claim 1 inwhich the allowance has a thickness of between 0.1 and 1.0 mm.
 3. Themethod according to claim 2 in which the allowance has a thickness ofbetween 0.20 and 0.25 mm.
 4. The method according to claim 1 in whichthe subsequent processing comprises a tumbling step after the secondblanking step.
 5. The method according to claim 1 comprising, prior tothe first blanking step, the step of coining of the semi-finishedproduct to produce a coined semi-finished product.
 6. The methodaccording to claim 5 in which the coined semi-finished product comprisesat least a first pair of locating appendages for locating the coinedsemi-finished product on a die in order to perform the first blankingstep.
 7. The method according to claim 6 in which the coinedsemi-finished product comprises a second pair of locating appendages,the first pair being removed during the first blanking step and thesecond pair being removed during the second blanking step.
 8. A methodaccording to claim 7 in which the second pair of locating appendages ispositioned on surfaces of the semi-finished product which are to beprocessed further after the second blanking step and/or which are not inview upon completion of the processing.
 9. The method according to claim1 in which the final product is a portion of a spectacle frame.
 10. Themethod according to claim 1 in which the metal of the semi-finishedproduct is selected from brass, nickel silver, and aluminum.